Liquid crystal display device

ABSTRACT

A liquid crystal display device includes a first transparent substrate having a plurality of electrodes, a second transparent substrate, a liquid crystal interposed between the first transparent substrate and the second transparent substrate, an illumination light source disposed on a back side of the first transparent substrate, pixel regions arranged in a matrix, and a reflecting film formed between the first transparent substrate and the electrodes. The reflecting film has at least one light transmission aperture in each pixel region and without slits at positions corresponding to gaps between adjacent ones of the pixel regions.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 09/828,210, filedApr. 9, 2001, now U.S. Pat. No. 6,697,137, the subject matter of whichis incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to a semi-transmission/reflection-typeliquid crystal display device that displays an image by selectivelyusing transmission light and reflection light.

Being thin, light, and low in power consumption, liquid crystal displaydevices in which a liquid crystal display panel is used as an imagegenerating means are employed as display devices in a wide variety ofelectronic equipment, such as notebook-sized personal computers, wordprocessors, electronic notes, cellular phones, and camera-incorporatedvideo recorders.

In contrast to CRTs and plasma display panels, liquid crystal displaypanels display an image by controlling the quantity of light that hasentered the panel from the outside instead of emitting light by itself.When equipped with color filters of plural colors as light controlelements, liquid crystal display panels can display a color image ofmultiple colors.

Liquid crystal display devices that are used most commonly at presentare transmission-type devices in which an illumination light source,called a backlight that uses a fluorescent tube, is provided on the backside of a liquid crystal panel, and an image is displayed by controllingthe quantity of light (part of light emitted from the backlight) thatpasses through the liquid crystal panel.

However, in such transmission-type liquid crystal display devices, thepower consumption of the backlight accounts for approximately one halfof the total power consumption. This is a major factor in shortening theusable time in a case where portable electronic apparatuses asexemplified above are of a battery-driven type. Transmission-type liquidcrystal display devices have another problem, in that, when they areused in a bright outdoor environment, for example, ambient light isreflected by the surface of the display area and a displayed imagebecomes hard to recognize.

Among liquid crystal display devices that are always used in a carriedstate in a bright environment such as found outdoors, there arereflection-type liquid crystal display devices that usually do not use abacklight, but are equipped with a reflection plate, and control thequantity of reflection light (part of ambient light) with the liquidcrystal layer. An example of such liquid crystal display devices is onethat performs both transmission-type display and reflection-type displayusing a semitransparent reflecting film (e.g., Japanese UnexaminedPatent Publication No. Hei. 7-333598).

Another example of the above type of liquid crystal display device isone in which each pixel electrode is composed of two regions thatcomprise a reflection region and a transmission region (e.g., JapaneseUnexamined Patent Publication No. Hei. 7-333598).

However, in the above conventional liquid crystal display devices, thedisplay quality varies depending on the use environment(light-source-related environment). That is, a display that is performedby using reflection light (reflection light mode) and a display that isperformed by using transmission light (transmission light mode) havingdifferent contrast ratios. Further, a coloration phenomenon may occur inblack-and-white display and hue deviation may occur in color display.The difference in contrast ratio is caused by the fact that the blackdisplay luminance (off transmittance) and the white display luminance(on transmittance) are different between the case where reflection lightis used and the case where transmission light is used. This phenomenonlowers the legibility of a displayed image. The hue deviation is aphenomenon that the hue shifts to the bluish side particularly in thecase where transmission light is used. This deteriorates the colorreproduction performance.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problems in theart, and an object of the invention is therefore to provide a liquidcrystal display device which is capable of image display with a largecontrast ratio in both a transmission display mode and a reflectiondisplay mode, as well as being capable of good color display in bothdisplay modes.

To attain the above object, the invention provides the followingconfiguration. A liquid crystal is interposed between a firsttransparent substrate having first electrodes and a second transparentsubstrate having other electrodes that are opposed to the firstelectrodes. Pixel regions are formed at portions where the firstelectrodes and the other electrodes are opposed to each other. Asemitransparent reflecting film (or an opaque reflecting film) is formedbetween the first transparent substrate and the first electrodes. Thesemitransparent reflecting film is formed with light transmissionapertures in each pixel region. Or, the semitransparent reflecting filmis formed with slits at positions corresponding to the gaps betweenadjacent pixel regions. With the above measure, part of the illuminationlight that comes from the first transparent substrate side is introducedto the liquid crystal through the light transmission apertures or theslits.

An opaque reflecting film may be formed instead of a semitransparentreflecting film. In the case of an opaque reflecting film, thecombination of the opaque reflecting film and the light transmissionapertures serves as the above-mentioned “semitransparent reflectingfilm.” In the case of the semitransparent reflecting film, thesemitransparent reflecting film itself and the light transmissionapertures serve as the above-mentioned “semitransparent reflectingfilm.” The same interpretation applies to the term “semitransparentreflecting film” that will be used in the following description andembodiments.

With the above configuration, in the transmission light mode, part ofthe light that comes from the outside of the first transparent substrateis output from the second transparent substrate after passing throughcolor filters. Therefore, not only is the legibility of a display imageimproved, but also a hue deviation in transmission light is decreased,which improves the color reproduction performance.

Where the semitransparent reflecting film also occupies the portionscorresponding to the gaps between the adjacent pixel regions, thecontrast in the transmission light mode is increased.

The peripheral portions of adjacent ones of color filter layers that areformed between the second transparent substrate and the other electrodesmay overlap with each other to provide a light shield function. Sincethe overlapping portions of the color filter layers serve as lightshield layers, the contrast is increased.

A light absorption film may be formed under the slits that are formed onthe side of the first transparent substrate, or the slits may be chargedwith a light absorption film. This prevents color mixture betweenadjacent pixels and hence increases the contrast.

A semi-transmission/reflection-type liquid crystal display device isconstructed by disposing an illumination light source on the back sideof the first transparent substrate of the above liquid crystal displaypanel. In an environment where the brightness is sufficiently high, thesemi-transmission/reflection-type liquid crystal display device is usedin the reflection light mode by turning off the illumination lightsource. In a dark environment, it is used in the transmission light modeby turning on the illumination light source. The color reproductionperformance is improved in either mode.

In the semi-transmission/reflection-type liquid crystal display deviceusing the above liquid crystal display panel, an upper polarizer and alower polarizer are formed on the display screen side (i.e., the secondtransparent substrate side) of the liquid crystal display panel and onthe side opposite to it (i.e., the first transparent substrate side),respectively, and their optical absorption axes (polarizing axes) areset approximately perpendicular to each other.

A first alignment layer is formed on the inside surface of the substrate(first transparent substrate) provided on the illumination lightincidence side (in the transmission light mode), and the alignment axisof the first alignment layer and the absorption axis of the lowerpolarizer are set approximately parallel with each other. The blackdisplay luminance (off transmittance) that is obtained when blackdisplay voltages are applied to the pixel electrodes of the liquidcrystal display panel is made low and the white display luminance (ontransmittance) that is obtained when white display voltage are appliedto the pixel electrodes is made high, whereby the contrast ratio of adisplay image is increased irrespective of the display mode.

A first upper phase plate and a second upper phase plate are formed onthe substrate provided on the display screen side of the liquid crystaldisplay panel and their drawing axes are deviated from each other byabout 30° (30°±20°), whereby light that has passed through the liquidcrystal layer is converted into approximately linearly polarized light.This prevents a coloration phenomenon in black-and-white display and huedeviation in color display (neutralization of display color) and therebyenables high-quality color reproduction that is free of hue deviation.

Typical configurations according to the invention are as follows.

(1) A liquid crystal display device comprising:

a first transparent substrate having a plurality of first electrodes;

a second transparent substrate having a plurality of second electrodes(other electrodes) that are opposed to the first electrodes;

a liquid crystal interposed between the first transparent substrate andthe second transparent substrate;

an illumination light source disposed on the back side of the firsttransparent substrate;

pixel regions formed at portions where the first electrodes and thesecond electrodes are opposed to each other; and

a reflecting film formed between the first transparent substrate and thefirst electrodes, the reflecting film having one or a plurality of lighttransmission apertures in each pixel region and not having slits atpositions corresponding to gaps between adjacent ones of the pixelregions.

(2) In configuration (1), color filter layers are further providedbetween the second transparent substrate and the second electrodes, andperipheral portions of adjacent ones of the color filter layers overlapwith each other at positions corresponding to the gaps between adjacentones of the pixel regions.

(3) A liquid crystal display device comprising:

a first transparent substrate having a plurality of first electrodes;

a second transparent substrate having a plurality of second electrodesthat are opposed to the first electrodes;

a liquid crystal interposed between the first transparent substrate andthe second transparent substrate;

illumination light source disposed on the back side of the firsttransparent substrate;

pixel regions formed at portions where the first electrodes and thesecond electrodes are opposed to each other;

a reflecting film formed between the first transparent substrate and thefirst electrodes, the reflecting film having one or a plurality of lighttransmission apertures in each pixel region and slits at positionscorresponding to gaps between adjacent ones of the pixel regions; and

a light absorption film formed between the first transparent substrateand the reflecting film at positions corresponding to the slits.

(4) A liquid crystal display device comprising:

a first transparent substrate having a plurality of first electrodes;

a second transparent substrate having a plurality of second electrodesthat are opposed to the first electrodes;

a liquid crystal interposed between the first transparent substrate andthe second transparent substrate;

illumination light source disposed on the back side of the firsttransparent substrate;

pixel regions formed at portions where the first electrodes and thesecond electrodes are opposed to each other;

a reflecting film formed between the first transparent substrate and thefirst electrodes, the reflecting film having one or a plurality of lighttransmission apertures in each pixel region and slits at positionscorresponding to gaps between adjacent ones of the pixel regions; and

a light absorption film with which the slits are charged.

(5) In each of configurations (I)–(4), the reflecting film is an opaquereflecting film.

(6) In each of configurations (1)–(4), the reflecting film is asemitransparent reflecting film.

(7) A liquid crystal is interposed between a first transparent substratehaving first electrodes and a second transparent substrate having otherelectrodes that are opposed to the first electrodes. Pixel regions areformed at portions where the first electrodes and the other electrodesare opposed to each other. A semitransparent reflecting film that isformed with light transmission apertures in each pixel region is formedbetween the first transparent substrate and the first electrodes.

(8) Color filter layers in which the peripheral portions of the adjacentcolor filter layers overlap with each other are provided between thefirst transparent substrate and the first electrodes and the overlappingperipheral portions serve as light shield films located at positionscorresponding to the gaps between adjacent pixel regions.

(9) A liquid crystal is interposed between a first transparent substratehaving first electrodes and a second transparent substrate having otherelectrodes that are opposed to the first electrodes. Pixel regions areformed at portions where the first electrodes and the other electrodesare opposed to each other. A semitransparent reflecting film that isformed with light transmission apertures on each pixel region and slitsextending along the peripheries of the pixel regions are formed betweenthe first transparent substrate and the first electrodes.

(10) A light absorption film is formed under the slits (i.e., on theside of the first transparent substrate), or the slits are charged witha light absorption film.

(11) A semi-transmission/reflection-type liquid crystal display deviceis constructed by disposing an illumination light source on the backside of the first transparent substrate of the liquid crystal displaypanel of each of configurations (7)–(10).

(12) In configuration (11), an upper polarizer and a lower polarizerwhose absorption axes (polarizing axes) are set approximatelyperpendicular to each other are formed on the surface on the secondtransparent substrate side and the surface on the first transparentsubstrate side, respectively. A first alignment layer and a secondalignment layer are formed at the boundaries between the liquid crystaland the inside surfaces of the first transparent substrate and thesecond transparent substrate, respectively, and the alignment axis ofthe first alignment layer and the absorption axis of the lower polarizerare set approximately parallel with each other. A first upper phaseplate and a second upper phase plate whose drawing axes are deviatedfrom each other by about 30° (30°±20°) are formed on the outside surfaceof the second transparent substrate.

With the above configuration, the black display luminance (offtransmittance) that is obtained when a black display voltage is appliedto the first pixel electrodes and the other pixel electrodes of theliquid crystal display panel is made low and the white display luminance(on transmittance) that is obtained when white display voltages areapplied to the pixel electrodes is made high, whereby the contrast ratioof a display image is increased irrespective of the display mode.Therefore, the legibility is improved and a high-quality liquid crystaldisplay panel can be realized.

A diffusion layer is provided between the first upper phase plate andthe second upper phase plate. A known diffusion sheet may be used as thediffusion layer. However, if the diffusion layer is formed by mixinglight diffusing particles into an adhesive for bonding the first andsecond upper phase plates to each other, the optical loss is minimizedand bright display can thereby be attained.

Each of the above configurations makes it possible to produce a bright,clear image having a large contrast ratio or a high-quality color imagethat is free of hue deviation in both an environment having brightambient light and a dark environment by selectively using transmissionlight and reflection light.

The invention is not limited to the above configurations or theembodiments described below. It goes without saying that variousmodifications are possible without departing from the spirit and scopeof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic diagrams showing the configuration of aliquid crystal display panel according to a first embodiment of thepresent invention, in which FIG. 1A is a sectional view of its main partand FIG. 1B is a plan view of the main part of a first transparentsubstrate as viewed in the direction indicated by arrows A in FIG. 1A;

FIGS. 2A and 2B are schematic diagrams showing the configuration of aliquid crystal display panel according to a second embodiment of theinvention, in which FIG. 2A is a sectional view of its main part andFIG. 2B is a plan view of the main part of a first transparent substrateas viewed in the direction indicated by arrows B in FIG. 2A;

FIGS. 3A and 3B are schematic diagrams showing the configuration of aliquid crystal display panel according to a third embodiment of theinvention, in which FIG. 3A is a sectional view of its main part andFIG. 3B is a plan view of the main part of a first transparent substrateas viewed in the direction indicated by arrows C in FIG. 3A;

FIGS. 4A and 4B are schematic diagrams showing the configuration of aliquid crystal display panel according to a fourth embodiment of theinvention, in which FIG. 4A is a sectional view of its main part andFIG. 4B is a plan view of the main part of a first transparent substrateas viewed in the direction indicated by arrows D in FIG. 4A;

FIGS. 5A–5D are diagrams which show other exemplary shapes andarrangements of light transmission apertures that are formed in asemitransparent reflecting film of the liquid crystal display panelaccording to the invention;

FIG. 6 is a schematic sectional view of asemi-transmission/reflection-type liquid crystal display panel;

FIG. 7 is a schematic diagram showing the arrangement of optic axes ofthe liquid crystal display panel shown in FIG. 6;

FIG. 8 is a schematic sectional view showing the configuration of airexemplary personal digital assistant incorporating a touch panel thatuses the liquid crystal display panel according to the invention; and

FIG. 9 is a perspective view showing the configuration of an exemplaryportable digital assistant that is an electronic apparatus incorporatingthe liquid crystal display device according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Liquid crystal display panels according to embodiments of the presentinvention will be hereinafter described in detail with reference to theaccompanying drawings.

FIGS. 1A and 1B are schematic diagrams showing the configuration of aliquid crystal display panel according to a first embodiment of theinvention. FIG. 1A is a sectional view of its main part and FIG. 1B is aplan view of the main part of a first transparent substrate as viewed inthe direction indicated by arrows A in FIG. 1A. Alignment layers thatdetermine the initial alignment of a liquid crystal, polarizers, andphase plates are not shown in FIGS. 1A and 1B.

The liquid crystal display panel PNL is of a passive matrix type(STN-LCD) in which a liquid crystal layer (also referred to simply as“liquid crystal”) LC is interposed between a first transparent substrateSUB1 and a second transparent substrate SUB2.

The first transparent substrate SUB1 is a hard plate, more specifically,a glass plate in this embodiment. A semitransparent reflecting film T/Ris formed on the inside surface of the first transparent substrate SUB1.A plurality of first electrodes (transparent pixel electrodes) ITO1 thatconstitute pixels are formed parallel with each other on thesemitransparent reflecting film T/R with an overcoat layer OC1interposed inbetween. The first electrodes ITO1 may be made of ITO(indium tin oxide) or IZO (indium zinc oxide). ITO is employed in thisembodiment. A lower alignment layer (not shown) is formed so as to coverthe first electrodes ITO1 and is subjected to alignment processing, suchas rubbing.

The second transparent substrate SUB2 is also a glass plate. Colorfilters CF of three colors (e.g., R, G, and B) are formed on the insidesurface of the second transparent substrate SUB2 at such positions as tobe opposed to the first electrodes ITO1. Adjacent ones of the colorfilters CF overlap with each other, whereby a light shield function(i.e., a function of a vertical black matrix (vertical BM)) is obtained.The overlap width is set approximately equal to the width of each of thefirst electrodes ITO1.

An overcoat layer OC2 is formed so as to cover the color filters CF, andthe other electrodes ITO2 are formed on the overcoat layer OC2 (on theside of the liquid crystal LC). The other electrodes ITO2 are made ofthe same conductive material as that of the first electrodes ITO1.

The other electrodes ITO2 are disposed so as to cross the firstelectrodes ITO1 that are formed on the first transparent substrate SUB1.Unit pixels are formed at the crossing portions.

Symbol BM(H) in FIG. 1B denotes horizontal light shield films(horizontal BM) that are formed on the second transparent substrate SUB2so as to traverse the other electrodes ITO2. Each region that isenclosed by the vertical BM and the horizontal BM and has an area X×Y isa pixel region of one color (i.e., a unit pixel) corresponding to onecolor filter.

The semitransparent reflecting film T/R is formed on the firsttransparent substrate SUB1 with an Al alloy or an Ag alloy basicallyover the entire surface and has several light transmission apertures APin each pixel region having the area X×Y. Although in this embodimentfour circular light transmission apertures AP are formed in each pixelregion, the number and the shape of light transmission apertures AP arearbitrary, as will be described later.

The liquid crystal LC that is interposed between the first transparentsubstrate SUB1 and the second transparent substrate SUB2 is an STN(super twisted nematic) liquid crystal.

In this embodiment, the color filters CF are formed on the secondtransparent substrate SUB2 by a photolithography process using apigment-dispersed resist. However, the color filters CF may be formed byother known methods, such as a method in which coloring is performed byusing dyes as dyeing agents, an ink jetting method, and a method ofattaching color sheets on which three colors are printed in advance.

The overcoat layers OC1 and OC2 are provided for such purposes aspreventing deterioration in the quality of the semitransparentreflecting film T/R, the color filters CF, and the material of theliquid crystal LC and securing uniform alignment of the liquid crystalLC by planarizing the surfaces. Examples of the material of the overcoatlayers OC1 and OC2 are a thermosetting acrylic resin, an urethane resin,a polyglycidyl methacrylate resin, and a silica-type inorganic material.

As described above, according to the embodiment, the light transmissionapertures AP are formed in the semitransparent reflecting film T/R,whereby the luminance in the transmission light mode is increased. Thecircular shape of the light transmission apertures AP minimizes avariation in forming the semitransparent reflecting film T/R byphotolithography and etching, whereby the area of the light transmissionapertures AP can be uniformized easily.

Since the semitransparent reflecting film T/R occupies the gaps betweenthe first electrodes ITO1 operating as the pixel electrodes (i.e., thereare no slits in the semitransparent reflecting film T/R at positionscorresponding to the gaps between the adjacent pixel regions), when abacklight that is provided on the back side of the liquid crystaldisplay panel is turned on, leakage of light through the gaps betweenthe first electrodes ITO1 can be prevented. This increases the contrastin the transmission light mode.

FIGS. 2A and 2B are schematic diagrams showing the configuration of aliquid crystal display panel according to a second embodiment of theinvention. FIG. 2A is a sectional view of its main part and FIG. 2B is aplan view of the main part of a first transparent substrate as viewed inthe direction indicated by arrows B in FIG. 2A. Alignment layers thatdetermine the initial alignment of a liquid crystal, polarizers, andphase plates are not shown in FIGS. 2A and 2B.

As in the case of the first embodiment, the liquid crystal display panelPNL is of a passive matrix type (STN-LCD) in which a liquid crystal LCis interposed between a first transparent substrate SUB1 and a secondtransparent substrate SUB2.

As in the case of the first embodiment, both the first transparentsubstrate SUB1 and the second transparent substrate SUB2 are provided inthe form of a glass plate. A semitransparent reflecting film T/R isformed on the inside surface of the first transparent substrate SUB1. Aplurality of first electrodes ITO1 that constitute pixels are formedparallel with each other on the semitransparent reflecting film T/R withan overcoat layer OC1 interposed in between. As in the case of the firstembodiment, the first electrodes ITO1 are made of ITO. A lower alignmentlayer (not shown) is formed so as to cover the first electrodes ITO1 andis subjected to alignment processing, such as rubbing.

Color filters CF of three colors (e.g., R, G, and B) are formed on theinside surface of the second transparent substrate SUB2 at suchpositions as to be opposed to the first electrodes ITO1. Adjacent onesof the color filters CF overlap with each other, whereby a light shieldfunction (i.e., a function of a vertical black matrix (vertical BM)) isobtained. The overlap width is set approximately equal to the width ofeach of the first electrodes ITO 1.

An overcoat layer OC2 is formed so as to cover the color filters CF, andthe other electrodes ITO2 are formed on the overcoat layer OC2 (on theside of the liquid crystal LC). The other electrodes ITO2 are made ofthe same conductive material as that of the first electrodes ITO1.

The other electrodes ITO2 are disposed so as to cross the firstelectrodes ITO1 that are formed on the first transparent substrate SUB1.Unit pixels are formed at the crossing portions.

Symbol BM(H) in FIG. 2B denotes horizontal light shield films(horizontal BM) that are formed on the second transparent substrate SUB2so as to traverse the other electrodes ITO2. Each region that isenclosed by the vertical BM and the horizontal BM and has an area X×Y isa pixel region of one color (i.e., a unit pixel) corresponding to onecolor filter.

The semitransparent reflecting film T/R is formed on the firsttransparent substrate SUBI with the same material as used in the firstembodiment, and is formed with slits SLT at positions corresponding tothe gaps between adjacent first electrodes ITO1. That is, thesemitransparent reflecting film T/R is divided into portionscorresponding to the pixel regions.

The semitransparent reflecting film T/R has several light transmissionapertures AP in each pixel region having the area X×Y. Although in thisembodiment four circular light transmission apertures AP are formed ineach pixel region, the number and the shape of light transmissionapertures AP are arbitrary, as will be described later.

The liquid crystal LC that is interposed between the first transparentsubstrate SUB1 and the second transparent substrate SUB2 is an STN(super twisted nematic) liquid crystal.

In this embodiment, the color filters CF are formed on the secondtransparent substrate SUB2 by a photolithography process using apigment-dispersed resist. However, the color filters CF may be formed byother known methods, such as a method in which coloring is performed byusing dyes as dyeing agents, an ink setting method, and a method ofattaching color sheets on which three colors are printed in advance.

The overcoat layers OC1 and OC2 are provided for such purposes aspreventing deterioration in the quality of the semitransparentreflecting film T/R, the color filters CF, and the material of theliquid crystal LC and securing uniform alignment of the liquid crystalLC by planarizing the surfaces. Examples of the material of the overcoatlayers OC1 and OC2 are a thermosetting acrylic resin, an urethane resin,a polyglycidyl methacrylate resin, and a silica-type inorganic material.

As described above, according to the embodiment, the light transmissionapertures AP are formed in the semitransparent reflecting film T/R,whereby the luminance in the transmission light mode is increased. Thecircular shape of the light transmission apertures AP minimizes avariation in forming the semitransparent reflecting film T/R byphotolithography and etching, whereby the area of the light transmissionapertures AP can be uniformized easily.

Since the slits SLT are formed in the semitransparent reflecting filmT/R at the positions corresponding to the gaps between the oneelectrodes ITOI as the pixel electrodes (i.e., the gaps between theadjacent pixel regions: slits), when a backlight that is provided on theback side of the liquid crystal display panel is turned on, part of thelight emitted from the backlight can be introduced into the liquidcrystal LC. This increases the brightness in the transmission lightmode.

FIGS. 3A and 3B are schematic diagrams showing the configuration of aliquid crystal display panel according to a third embodiment of theinvention. FIG. 3A is a sectional view of its main part and FIG. 3B is aplan view of the main part of a first transparent substrate as viewed inthe direction indicated by arrows C in FIG. 3A. Alignment layers thatdetermine the initial alignment of a liquid crystal, polarizers, andphase plates are not shown in FIGS. 3A and 3B.

As in the case of the first and second embodiments, the liquid crystaldisplay panel PNL is of a passive matrix type (STN-LCD) in which aliquid crystal LC is interposed between a first transparent substrateSUB1 and a second transparent substrate SUB2.

As in the case of the first and second embodiments, both of the firsttransparent substrate SUBI and the second transparent substrate SUB2 areprovided as a glass plate. A semitransparent reflecting film T/R isformed on the inside surface of the first transparent substrate SUB1. Aplurality of first electrodes ITO1 that constitute pixels are formedparallel with each other on the semitransparent reflecting film T/R withan overcoat layer OCI interposed in between. As in the case of the firstand second embodiments, the one electrodes ITO1 are made of ITO. A loweralignment layer (not shown) is formed so as to cover the firstelectrodes ITO1 and is subjected to alignment processing, such asrubbing.

Color filters CF of three colors (e.g., R, G, and B) are formed on theinside surface of the second transparent substrate SUB2 at suchpositions as to be opposed to the first electrodes ITO1.

An overcoat layer OC2 is formed so as to cover the color filters CF, andthe other electrodes ITO2 are formed on the overcoat layer OC2 (on theside of the liquid crystal LC). The other electrodes ITO2 are made ofthe same conductive material as that of the first electrodes ITO1.

The other electrodes ITO2 are disposed so as to cross the firstelectrodes ITO1 that are formed on the first transparent substrate SUB1.Unit pixels are formed at the crossing portions.

A light shield film (black matrix BM) consisting of a horizontal BM(BM(H)) and a vertical BM (BM(V)) is formed on the first transparentsubstrate SUB1. Each region that is enclosed by the horizontal BM(BM(H)) and the vertical BM (BM(V)) and has an area X×Y is a pixelregion of one color (i.e., a unit pixel) corresponding to one colorfilter.

The semitransparent reflecting film T/R is formed on the light shieldfilm BM that is formed on the first transparent substrate SUB1. Thesemitransparent reflecting film T/R is made of the same material as usedin the first and second embodiments, and is formed with slits SLT atpositions corresponding to the gaps between the adjacent firstelectrodes ITO1. The slits SLT expose parts of the light shield film BM,and the exposed parts of the light shield film BM separate the pixelregions. The light shield film BM can be formed by a knownphotolithography technique in which a light shield material mixed with aphotoresist is applied and then exposed to light through a photomaskhaving a prescribed opening pattern. The light shield film BM can alsobe formed by screen printing.

In this embodiment, the effective width (optical width) of the lightshield film BM is determined by the processing accuracy in forming theslits SLT later in the semitransparent reflecting film T/R. Therefore,satisfactory results are obtained as long as the width of the lightshield film BM is larger than the width of the gaps between the adjacentfirst electrodes ITO1 that are formed on the overcoat layer OC1. Forthis reason, the light shield film BM need not be formed with highaccuracy, and hence the above-mentioned printing method is sufficient.

The semitransparent reflecting film T/R has several light transmissionapertures AP in each pixel region having the area X×Y. Although in thisembodiment four circular light transmission apertures AP are formed ineach pixel region, the number and the shape of light transmissionapertures AP are arbitrary, as will be described later.

The liquid crystal LC that is interposed between the first transparentsubstrate SUB1 and the second transparent substrate SUB2 is an STN(super twisted nematic) liquid crystal.

In this embodiment, the color filters CF are formed on the secondtransparent substrate SUB2 by a photolithography process using apigment-dispersed resist. However, the color filters CF may be formed byother known methods, such as a method in which coloring is performed byusing dyes as dyeing agents, an ink jetting method, and a method ofattaching color sheets on which three colors are printed in advance.

The overcoat layers OC1 and OC2 are provided for such purposes aspreventing deterioration in the quality of the semitransparentreflecting film T/R, the light shield film BM, the color filters CF, andthe material of the liquid crystal LC and securing uniform alignment ofthe liquid crystal LC by planarizing the surfaces. Examples of thematerial of the overcoat layers OC1 and OC2 are a thermosetting acrylicresin, an urethane resin, a polyglycidyl methacrylate resin, and asilica-type inorganic material.

As described above, according to the embodiment, the light transmissionapertures AP are formed in the semitransparent reflecting film T/R,whereby the luminance in the transmission light mode is increased. Thecircular shape of the light transmission apertures AP minimizes avariation in forming the semitransparent reflecting film T/R byphotolithography and etching, whereby the area of the light transmissionapertures AP can be uniformized easily.

Since the slits SLT are formed in the semitransparent reflecting filmT/R at the positions corresponding to the gaps between the firstelectrodes ITO1 operating as the pixel electrodes (i.e., the gapsbetween the adjacent pixel regions: slits) and the light shield film BMis formed in association with the slits SLT, when a backlight that isprovided on the back side of the liquid crystal display panel is turnedon, leakage of light that is emitted from the backlight is prevented andlight beams of adjacent pixel regions can be separated from each other,leading to an increase in contrast.

FIGS. 4A and 4B are schematic diagrams showing the configuration of aliquid crystal display panel according to a fourth embodiment of theinvention. FIG. 4A is a sectional view of its main part and FIG. 4B is aplan view of the main part of a first transparent substrate as viewed inthe direction indicated by arrows D in FIG. 4A. Alignment layers thatdetermine the initial alignment of a liquid crystal, polarizers, andphase plates are not shown in FIGS. 4A and 4B.

As in the case of the first to third embodiments, the liquid crystaldisplay panel PNL is of a passive matrix type (STN-LCD) in which aliquid crystal LC is interposed between a first transparent substrateSUBI and a second transparent substrate SUB2.

As in the case of the first to third embodiments, both of the firsttransparent substrate SUBI and the second transparent substrate SUB2 areprovided in the form of a glass plate. A semitransparent reflecting filmT/R is formed on the inside surface of the first transparent substrateSUB1. A plurality of first electrodes ITO1 that constitute pixels areformed parallel with each other on the semitransparent reflecting filmT/R with an overcoat layer OCI interposed in between. As in the case ofthe first to third embodiments, the first electrodes ITO1 are made ofITO. A lower alignment layer (not shown) is formed so as to cover thefirst electrodes ITO1 and is subjected to alignment processing, such asrubbing.

Color filters CF of three colors (e.g., R, G, and B) are formed on theinside surface of the second transparent substrate SUB2 at suchpositions as to be opposed to the first electrodes ITO1.

An overcoat layer OC2 is formed so as to cover the color filters CF, andthe other electrodes ITO2 are formed on the overcoat layer OC2 (on theside of the liquid crystal LC). The other electrodes ITO2 are made ofthe same conductive material as that of the first electrodes ITO1.

The other electrodes ITO2 are disposed so as to cross the firstelectrodes ITO1 that are formed on the first transparent substrate SUB1.Unit pixels are formed at the crossing portions.

A light shield film (black matrix BM) consisting of a horizontal BM(BM(H)) and a vertical BM (BM(V)) is formed on the first transparentsubstrate SUB1. Each region that is enclosed by the horizontal BM(BM(H)) and the vertical BM (BM(V)) and has an area X×Y is a pixelregion of one color (i.e., a unit pixel) corresponding to one colorfilter.

The semitransparent reflecting film T/R is made of the same material asused in the first to third embodiments, and is formed with slits SLT atpositions corresponding to the gaps between the adjacent firstelectrodes ITO1. The slits SLT are charged with the light shield film BMand the light shield film BM separates the pixel regions.

The semitransparent reflecting film T/R has several light transmissionapertures AP in each pixel region having the area X×Y. Although in thisembodiment four circular light transmission apertures AP are formed ineach pixel region, the number and the shape of light transmissionapertures AP are arbitrary, as will be described later.

The light shield film BM can be formed by a photolithography techniquein which a light shield material mixed with a photoresist is appliedafter formation of the slits SLT and the light transmission apertures APand then back exposure is performed from the first transparent substrateSUB1 side to set and leave parts of the light shield material existingin the slits SLT.

In the above process, the light shield material is prevented fromleaving in the light transmission apertures AP by covering the lighttransmission apertures AP with a proper mask during the exposure orduring the application of the light shield material.

The liquid crystal LC that is interposed between the first transparentsubstrate SUB1 and the second transparent substrate SUB2 is an STN(super twisted nematic) liquid crystal.

In this embodiment, the color filters CF are formed on the secondtransparent substrate SUB2 by a photolithography process using apigment-dispersed resist. However, the color filters CF may be formed byother known methods, such as a method in which coloring is performed byusing dyes as dyeing agents, an ink jetting method, and a method ofattaching color sheets on which three colors are printed in advance.

The overcoat layers OC1 and OC2 are provided for such purposes aspreventing deterioration in the quality of the semitransparentreflecting film T/R, the light shield film BM, the color filters CF, andthe material of the liquid crystal LC and securing uniform alignment ofthe liquid crystal LC by planarizing the surfaces. Examples of thematerial of the overcoat layers OC1 and OC2 are a thermosetting acrylicresin, an urethane resin, a polyglycidyl methacrylate resin, and asilica-type inorganic material.

As described above, according to the embodiment, the light transmissionapertures AP are formed in the semitransparent reflecting film T/R,whereby the luminance in the transmission light mode is increased. Thecircular shape of the light transmission apertures AP minimizes avariation in forming the semitransparent reflecting film T/R byphotolithography and etching, whereby the area of the light transmissionapertures AP can be uniformized easily.

Since the slits SLT are formed in the semitransparent reflecting filmT/R at the positions corresponding to the gaps between the firstelectrodes ITO1 operating as the pixel electrodes (i.e., the gapsbetween the adjacent pixel regions: slits) and the slits SLT are chargedwith the light shield film BM, when a backlight that is provided on theback side of the liquid crystal display panel is turned on, leakage oflight that is emitted from the backlight is prevented and light beams ofadjacent pixel regions can be separated from each other, leading toincrease in contrast.

FIGS. 5A–5D show other exemplary shapes and arrangements of lighttransmission apertures AP that are formed in the semitransparentreflecting film T/R of the liquid crystal display panel according to theinvention. A unit pixel portion (X×Y) of the semitransparent reflectingfilm T/R is shown in FIGS. 5A–5D.

Although in each of the above embodiments the light transmissionapertures AP that are formed in the semitransparent reflecting film TIRare circular apertures from the viewpoint of processing accuracy, theinvention is not limited to such a case. A feature of the inventionresides in that parts of light emitted from an illumination light sourcethat is provided on the back side of the first transparent substrateSUB1 are input to the liquid crystal LC through the pixel regions.

Therefore, in principle, the light transmission apertures AP that areformed in the semitransparent reflecting film T/R may be of any shape.The light transmission apertures AP can be formed by not only aphotolithography technique, but also known precision processingtechniques such as laser processing.

FIG. 5A shows a case where the light transmission apertures AP have anelliptical shape. FIG. 5B shows a case where they have a square shape.FIG. 5C shows a case where circular apertures having the same size ordifferent sizes are not arranged in line, but are staggered. FIG. 5Dshows a case where slit-shaped light transmission apertures AP arearranged.

The above shapes and arrangements of the light transmission apertures APmay be combined with each other. A proper number of light transmissionapertures AP having a proper shape may be arranged in a proper manner inaccordance with the electrode shape and the size of the liquid crystaldisplay panel.

Each of the above embodiments can increase the reflection light quantityin the reflection light mode and the transmission light quantity in thetransmission light mode, and can provide liquid crystal display panelsthat have increased brightness and contrast.

A light shield film BM may be formed between the color filters FC of therespective colors that are formed on the second transparent substrateSUB2. Such a light shield film BM may be made of chromium, chromiumoxide, a black resist called resin black, or a like material.

Next, specific exemplary structures of the liquid crystal display panelaccording to the invention and the liquid crystal display device usingit will be described. However, the invention is not limited to thestructures described below.

FIG. 6 is a schematic sectional view of asemi-transmission/reflection-type liquid crystal display panelcorresponding to the first embodiment of the invention, that wasdescribed above with reference to FIGS. 1A and 1B.

A first lower phase plate PD1 a, a second lower phase plate PDIb, and alower polarizer POLL are laid one on another in this order on theoutside surface of the first transparent substrate SUB1. The first lowerphase plate PD Ia is a λ4 plate and its Δnd is equal to 140 nm(measurement wavelength: 550 nm).

The second lower phase plate PD Ib is a λ2 plate and its Δnd is equal to270 nm (measurement wavelength: 550 nm).

On the other hand, a second upper phase plate PD2 b, a first upper phaseplate PD2 a, and an upper polarizer POL2 are laid one on another in thisorder on the surface of the second transparent substrate SUB2. Thesecond upper phase plate PD2 b and the first upper phase plate PD2 a arebonded together with an adhesive layer AD containing a light diffusingagent.

The bonding gap between the first transparent substrate SUB1 and thesecond transparent substrate SUB2, that is, the cell gap of the liquidcrystal LC, is maintained by spacers SP, such as polymer beads. Thespacers SP may be pole-like spacers that are fixedly formed on theinside surface of the first transparent substrate SUB1 or the secondtransparent substrate SUB2. Spacers SP may be omitted if the cell gapcan be maintained by another means.

FIG. 7 is a schematic diagram showing the arrangement of optic axes ofthe liquid crystal display panel shown in FIG. 6. The directions ofoptic axes (optical absorption axes (also referred to simply as“absorption”), drawing axes, alignment axes, etc.) of the respectivemembers constituting the liquid crystal display panel are indicated byarrows in respective layers. Angles are measured counterclockwise withrespect to the reference line X—X (corresponds to the horizontaldirection of the screen).

In FIG. 7, the absorption axis of the upper polarizer POL2 has an angle01 that is equal to 125°. The drawing axis of the second upper phaseplate PD2 b has an angle θ3 that is equal to 108°. The drawing axis ofthe first upper phase plate PD2 a has an angle θ2 that is equal to 72°.The drawing axis θ4 of the first lower phase plate PSIa has an angle θ4that is equal to 130°. The drawing axis of the second lower phase platePD1 b has an angle θ5 that is equal to 12.5°. The absorption axis of thelower polarizer POLI has an angle θ6 that is equal to 30°.

The alignment axis of the lower alignment layer ORI1 that is formed onthe first transparent substrate SUB1 has an angle θ7 that is equal to35°. The alignment axis of the upper alignment layer ORI2 that is formedon the second transparent substrate SUB2 has an angle θ8 that is equalto 35°. The twist angle θ_(T) of the liquid crystal LC is greater than240° and is written as 250° in FIG. 7.

FIG. 8 is a schematic sectional view showing the configuration of anexemplary personal digital assistant incorporating a touch panel thatuses the liquid crystal display panel according to the invention. Thispersonal digital assistant is equipped with the above-describedsemi-transmission/reflection-type liquid crystal display panel PNL andan illumination light source, that is, a backlight BL.

The backlight BL is formed on the back surface of the liquid crystaldisplay panel PNL. In a dark environment, illumination light that isemitted from the backlight BL is modulated in accordance with imagesignals being applied to the liquid crystal display panel PNL in passingthrough the liquid crystal display panel PNL. The image signals arevisualized when the illumination light is output to the display screenside of the liquid crystal display panel PNL. In a bright environment,the liquid crystal display panel PNL operates as a reflection-typeliquid crystal display panel that uses, as illumination light, ambientlight that enters the liquid crystal display panel PNL from the displayscreen side.

A touch panel TP that enables manual writing input by pressing it withthe tip of a pen or the like is formed on the display screen of theliquid crystal display panel PNL. Information is input through thedisplay screen of the liquid crystal display panel PNL by using thetouch panel TP.

That is, the liquid crystal display panel PNL has, on its back surface,the backlight BL that is composed of an approximately rectangular,transparent light guide plate GLB, a lamp CFL that is disposed along oneperiphery of the light guide plate GLB, and a lamp reflection sheet RFL.In the transmission display mode, light emitted from the backlight BL isdirected to the liquid crystal display panel PNL as it travels throughthe light guide plate GLB, and it illuminates the liquid crystal displaypanel PNL from the back side. Dots DOT or the like are formed on theback surface of the light guide plate GLB by printing or the like,whereby uniform luminance is obtained over the entire area of the liquidcrystal display panel PNL.

A reflection plate RF for returning, to the liquid crystal displaypanel. PNL, light that is output from the light guide plate GLB to theback side by fully reflecting it is provided on the back side of thelight guide plate GLB.

The backlight BL is attached to the liquid crystal display panel PNLwith a light quantity profile correcting member, such as a lightdiffusing film DDP or a prism plate (not shown) interposed in between.

Other light sources such as light-emitting diodes may be used in placeof the lamp CFL.

FIG. 9 is a perspective view showing the configuration of an exemplaryportable digital assistant (PDA) that is an electronic apparatusincorporating the liquid crystal display device according to theinvention. The portable digital assistant is composed of a main body MNthat accommodates a host computer HOST and a battery BAT and has akeyboard KB on its surface and a display section DP that incorporates aliquid crystal display device LCD and an inverter INV for a backlight.

A cellular phone PTP can be connected to the main body MN via aconnection cable L2, whereby communication with a person at a distantplace is enabled.

The liquid crystal display device LCD of the display section DP isconnected to the host computer HOST via an interface cable L1.

The display section DP has a pen holder PNH for accommodating an inputpen PN.

The liquid crystal display device allows a user to input informationthrough the keyboard KB, to input various kinds of information bypressing the surface of the touch panel, tracing a pattern displayedthereon, or writing characters etc. thereon with the input pen PN, toselect from pieces of information or processing functions displayed onthe liquid crystal display device PNL, and to perform other variousmanipulations.

The shape and the configuration of this type of portable digitalassistant is not limited to the illustrated ones. Portable digitalassistants having other various shapes, configurations and functions canbe constructed.

By using the liquid crystal display panel according to the invention asa liquid crystal display panel LCD2 that is used in the display sectionof the cellular phone PTP shown in FIG. 9, the cellular phone PTP canperform color data display that is highly legible.

As described above, according to the invention, in asemi-transmission/reflection-type liquid crystal display panel capableof always displaying a bright, clear full-color image irrespective ofthe brightness of an environment by selecting the reflection light modein a bright environment and the transmission light mode in a darkenvironment, bright, high-contrast image display as well as good colordisplay is enabled in each of the transmission light mode and thereflection light mode.

1. A liquid crystal display device comprising: a first transparentsubstrate having a plurality of electrodes; a second transparentsubstrate; a liquid crystal interposed between the first transparentsubstrate and the second transparent substrate; an illumination lightsource disposed on a back side of the first transparent substrate; pixelregions arranged in a matrix; and a reflecting film formed between thefirst transparent substrate and the electrodes, the reflecting filmhaving at least one light transmission aperture in each pixel region andwithout slits at positions corresponding to gaps between adjacent onesof the pixel regions; wherein the second transparent substrate has colorfilter layers, and wherein peripheral portions of adjacent ones of thecolor filter layers overlap with each other at positions correspondingto the gaps between adjacent ones of the pixel regions.
 2. A liquidcrystal display device according to claim 1, wherein the reflecting filmis an opaque reflecting film.
 3. A liquid crystal display deviceaccording to claim 1, wherein the reflecting film is a semitransparentreflecting film.
 4. A liquid crystal display device comprising: a firsttransparent substrate having a plurality of electrodes; a secondtransparent substrate; a liquid crystal interposed between the firsttransparent substrate and the second transparent substrate; anillumination light source disposed on a back side of the firsttransparent substrate; pixel regions arranged in a matrix; a reflectingfilm formed between the first transparent substrate and the electrodes,the reflecting film having at least one light transmission aperture ineach pixel region and slits at positions corresponding to gaps betweenadjacent ones of the pixel regions; and a light absorption film formedbetween the first transparent substrate and the reflecting film atpositions corresponding to the slits.
 5. A liquid crystal display deviceaccording to claim 4, wherein the reflecting film is an opaquereflecting film.
 6. A liquid crystal display device according to claim4, wherein the reflecting film is a semitransparent reflecting film. 7.A liquid crystal display device comprising: a first transparentsubstrate having a plurality of electrodes; a second transparentsubstrate; a liquid crystal interposed between the first transparentsubstrate and the second transparent substrate; an illumination lightsource disposed on a back side of the first transparent substrate; pixelregions arranged in a matrix; a reflecting film formed between the firsttransparent substrate and the electrodes, the reflecting film having atleast one light transmission aperture in each pixel region and slits atpositions corresponding to gaps between adjacent ones of the pixelregions; and a light absorption film with which the slits are charged.8. A liquid crystal display device according to claim 7, wherein thereflecting film is an opaque reflecting film.
 9. A liquid crystaldisplay device according to claim 7, wherein the reflecting film is asemitransparent reflecting film.
 10. A liquid crystal display deviceaccording to claim 7, wherein a surface of the light absorption film isdisposed at a height which is substantially at a height of a surface ofthe reflecting film.